1. Field of the Invention
The present invention relates to a drum for producing an electrodeposited metal foil such as a copper foil, an iron foil, a stainless steel foil, or the like on the circumferential surface of the drum.
2. Prior Art
Drums for forming electrodeposited metal foils are disclosed in Japanese Patent Publications Nos. 58(1983)-24507, 61(1986)-60149, and 62(1987)-233, for example.
One conventional drum includes an inner drum body and an outer skin. The outer skin is shrink-fitted over the inner drum body so that they are joined intimately together for reduced contact resistance therebetween. However, the inner circumferential surface of the outer skin cannot be machined to a nicety and tends to have surface irregularities because the outer skin is made of a roled material and has a large diameter. As a result, the outer circumferential surface of the inner drum body and the inner circumferential surface of the outer skin are not uniformly held against each other, but contact each other through surface irregularities. Therefore, a gap or clearance is present between the contacting surfaces of the inner drum body and the outer skin. Because of such a gap, a current which flows across the boundary surface region between the inner drum body and the outer skin during an electrodeposition process is liable to become irregular in intensity in different regions. Owing to the current irregularities, the metal foil deposited on the outer skin suffers thickness irregularities, abnormal metal deposition, and discolored spots known as hot spots due to localized overheating. Accordingly, no large current can be passed through the drum, and hence the metal foil cannot be produced at high speed.